Shaft Mechanical Lock for Pipeline Isolation Tools

ABSTRACT

A mechanical lock unit with a shaft lock assembly and method of achieving a self-lock mode for, e.g., hydraulically activated isolation plug module. The shaft lock assembly includes a teeth-form ring that surrounds a shaft. The teeth-form ring defines a plurality of teeth. A teeth-form split gripper assembly is positioned to surround the teeth-form ring. The teeth-form split gripper assembly has at least a first teeth-form split gripper and a second teeth-form split gripper with a spring therebetween for biasing the first teeth-form split gripper away from said second teeth-form split gripper. The first teeth-form split gripper and the second teeth form split gripper having an inner surface that defines a plurality of teeth for cooperative engagement with the plurality of teeth of the teeth-form ring.

CROSS-REFERENCE TO CO-PENDING APPLICATION

The present application is a continuation-in-part of, and claimspriority to, U.S. patent application Ser. No. 16/163,245, filed Oct. 17,2018, which is incorporated herein by reference.

FIELD OF THE INVENTION

The technical field of the invention is the mechanical field,specifically hydraulics. More particularly, the invention relates to alock for a hydraulically activated isolation plug module, when thelatter is used to isolate pipelines.

BACKGROUND OF THE INVENTION

A pipeline isolation module is provided for isolating pressurizedpipelines so that equipment maintenance, repairs, and replacements canbe done without bleeding down an entire system. Typical uses for apipeline isolation module include valve replacement, riser and midriserepair, tie-ins, dropped objection protection during construction,hydrotesting, and trap installation. The plug is used to isolate thepressure inside the pipeline by setting a sealing rubber packer againsta hydraulic cylinder. A typical isolation plug is locked by hydraulicactuation.

The pipeline isolation tool or plug is used to isolate pressure inside apipeline by setting a sealing rubber packer against a hydrauliccylinder. Typically, the isolation plug is locked by hydraulicactuation.

Pipeline isolation tools typically utilize hydraulic force to set thetool. Setting the tool securely is important to eliminate any rotationor axial movement of the shaft that can damage the shaft surface.

SUMMARY OF THE INVENTION

The pipeline isolation tool of the invention utilizes a shaft mechanicallock to mechanically lock the shaft of an isolation plug module fromaxial movement by using teeth engagement between a teeth-form ring onthe shaft and teeth-form split grippers in the mechanical lock unit.

The device of the invention can be used to mechanically lock theposition of the shaft by the engagement of two teeth-form parts, i.e.,the teeth-form split grippers in the mechanical lock unit and theteeth-form ring on the shaft. The spring-loaded lock piston functions tomaintain teeth engagement, which prevents the shaft from moving in anaxial direction. The teeth engagement differs from thread engagement,i.e., teeth engagement in the tool of the invention utilizes parallelteeth so that the shaft can still rotate without becoming disengaged.The tool of the invention can be used to mechanically lock ahydraulically activated isolation plug module for isolating pipelines.Mechanically locking the pipeline isolation tool acts as a safeguardwhen the hydraulic lock is lost, e.g., when there is a leak in thehydraulic system.

Engagement of the teeth-form split grippers together with the horizontalhold of the spring-loaded lock piston increases the ability to hold theshaft at very high loads.

The tool of the invention, therefore, increases reliability of the lockand, therefore, increases reliability of the seal, and also reduces therisk of losing the lock, thereby reducing the overall risk ofoperational failure.

The shaft mechanical lock may be used with isolation plugs having anexisting hydraulic system and offers the possibility to isolate from ahigh “back pressure”.

The tool of the invention can be used to mechanically lock the axialmovement of all types of shafts that have a high working load with highlock reliability. The mechanical lock provides an additional safeguardfor the hydraulic lock in addition to hydraulic actuation of a sealingpacker.

One advantage is that the teeth engagement as well as the horizontallock from the spring-loaded lock piston allow the dimensions of thedesign to be small while maintaining a high work load capacity.

In contrast to thread engagement, the parallel teeth engagement of thetool of the invention allows full rotation without losing engagement.

The tool of the invention includes teeth form split grippers, a teethform ring on the shoulder and a spring loaded lock piston in themechanical lock unit. Teeth-form split grippers are lifted up by thesprings between them. Teeth of the teeth-form split grippers arepositioned to engage teeth on a teeth-form ring on the shaft.

The teeth-form ring on the shaft may utilize a clearance fit with theshaft. The teeth-form ring on the shaft prevents damage to the shaftduring the lock/unlock process. A spring or elastomeric member at theend of the teeth-form ring may be provided to ensure that the teeth-formring can move slightly to the left or to the right to facilitate correctengagement with the teeth-form split grippers. In one embodiment, theteeth-form ring can be mounted in one step on the shaft and can be heldby a retaining ring or a lock nut at one end.

The teeth-form split grippers are assembled with a housing, lock piston,and lid as one unit (called the mechanical lock unit). The teeth-formring is assembled to the shaft, e.g., with a clearance fit, and held bya retaining ring or lock nut. The mechanical lock unit is then mountedat the locked position of the shaft.

In use, the isolation plug is pigged through a pipeline to an isolationset location. The mechanical lock unit is put into and unlock state.Hydraulic pressure is applied to the plug cylinder to move a plug pistonand set a rubber packer. After the packer is fully set, hydraulic forceinside the mechanical lock unit is released so that a spring forcepushes the lock piston of the mechanical lock unit into a locked state.The teeth engagement holds the isolation plug in place together with thehydraulic force inside the isolation plug.

In the normal locked state, the spring-loaded lock piston in themechanical lock unit compresses the teeth-form split gripper assemblyand the springs between teeth-form split grippers. Compression of theteeth-form split gripper assembly causes the teeth-form split grippersto engage with the teeth-form ring that holds and locks the axialmovement of the shaft. The parallel, circumferential orientation of theteeth, rather than a threaded orientation, allows the shaft to rotatewithout losing the engagement. Horizontal contact between a lock pistonand the split grippers, as well as teeth engagement, result intransferring all of the load of the plug piston to the strong lid of themechanical lock unit. Therefore, even though the dimensions of the toolof the invention may be small, the tool of the invention can hold a veryheavy load.

To unlock the mechanical lock unit, a hydraulic force is applied to thespring-loaded lock piston to overcome its spring force for pushing thepiston into an unlocked position. When there is no applied force fromthe lock piston, the teeth-form split grippers are lifted up by thesprings between the teeth form split grippers. Teeth engagement betweenthe split grippers of the teeth form split gripper assembly and theteeth form ring of the shaft is, therefore, removed and the shaft isunlocked and is free to move.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a cross-sectional view of a shaft surrounded by theteeth-form split grippers of the invention in an unlocked state.

FIG. 1B shows a cross-sectional view of a shaft surrounded by theteeth-form split grippers of FIG. 1A in a locked state.

FIG. 2 shows a first embodiment wherein the teeth-form ring is receivedon an end of a shaft.

FIG. 3 shows an end view of a second embodiment or bifurcated teeth formring.

FIG. 4 shows a side view of the bifurcated teeth form ring of FIG. 3.

FIG. 5 shows an elevation view of a third embodiment or slotted teethform ring.

FIG. 6 is a perspective view of an inline isolation plug module.

FIG. 7 is a cross-sectional view of the plug module of FIG. 6 shown inan unset state.

FIG. 8 is a cross-sectional view of the plug module of FIG. 6 shown in aset state wherein a piston is locked by the mechanical lock.

FIG. 9 shows an enlarged section of the plug module of FIG. 7 whereinthe second embodiment or bifurcated teeth-form ring of FIGS. 3 and 4received in a recessed area of a shaft as part of a mechanical lock unitshown in an unset state.

FIG. 10 shows an enlarged section of the plug module of FIG. 9 whereinthe second embodiment or bifurcated teeth-form ring of FIGS. 3 and 4received in a recessed area of a shaft as part of a mechanical lock unitshown in a set state.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Mechanical lock unit 10 includes shaft lock assembly 12. Shaft lockassembly 12 includes shaft 14. In one embodiment, shaft 14 defines firstdiameter portion 16, second diameter portion 18 and first annularsurface 20. First annular surface 20 is located between first diameterportion 16 and second diameter portion 18.

First resilient ring 22 surrounds second diameter portion 18 of shaft14. First resilient ring 22 has first side 24 that is adjacent to firstannular surface 20 of shaft 14.

Teeth form ring 30 surrounds second diameter portion 18 of shaft 14.Teeth form ring 30 has first end 32, second end 34, and outer surface 36(FIG. 2). Outer surface 36 defines plurality of teeth 38. First end 32is positioned adjacent to first resilient ring 22.

Still referring to FIG. 2, second resilient ring 50 surrounds seconddiameter portion 18 of shaft 14. Second resilient ring 50 is adjacent tosecond end 34 of teeth form ring 30.

Retain ring or lock ring 60 surrounds second diameter portion 18 ofshaft 14. Retain ring 60 is positioned adjacent to second resilient ring50.

A second embodiment, i.e., mechanical lock unit 100, includes shaft lockassembly 112 (FIGS. 3, 4). Shaft lock assembly 112 includes shaft 114.Shaft 114 defines first diameter portion 116, second diameter portion118, and third diameter portion 119 (FIG. 10). First diameter portion116 and third diameter portion 119 may be the same diameter. Shaft 114additionally defines first annular surface 120 between first diameterportion 116 and second diameter portion 118. Shaft 114 additionallydefines second annular surface 121 between second diameter portion 118and third diameter portion 119.

First resilient ring 122 surrounds second diameter portion 118 of shaft114. First resilient ring 122 has a first side adjacent to first annularsurface 120 of shaft 114.

A second embodiment of the teeth form ring is teeth form ring 130 (FIGS.3 and 4). Teeth form ring 130 surrounds second diameter portion 118 ofshaft 114. Teeth form ring 130 has first end 132 and second end 134.Teeth form ring 130 additionally has outer surface 136. Outer surface136 defines a plurality of teeth 138. Teeth form ring 138 is made up offirst half 140 and second half 142. First end 132 is located adjacent tofirst resilient ring 122. Teeth form ring 130 additionally includesfirst connector 144 for connecting first half 140 and second half 142.Teeth form ring 130 also includes second connector 146 for connectingfirst half 140 and second half 142.

Second resilient ring 150 surrounds second diameter portion 118 of shaft114. Second resilient ring 150 is positioned adjacent to second end 134of teeth form ring 130 and also adjacent to second annular surface 121of shaft 114.

A third embodiment of mechanical lock unit 210 includes shaft lockassembly designated 212 (FIG. 5). Shaft lock assembly 212 includesslotted teeth form ring 230. Shaft lock assembly 212 includes shaft 214.Shaft 214 includes bolt 215 that extends radially from shaft 214. Shaft214 defines a first diameter portion 216 and a second diameter portion218. Shaft 214 defines a first annular surface 220 between firstdiameter portion 216 and second diameter portion 218.

Slotted teeth form ring 230 defines slot 231 for receiving bolt 215.Slotted teeth form ring 230 may be constructed of two halves, similar toteeth form ring 130, above. Bolt 215 is provided for securing teeth formring 230 on shaft 214, and for allowing axial travel of slotted teethform ring 230 on shaft 214 to facilitate teeth engagement. Slotted teethform ring 230 has outer section 236 that defines a plurality of teeth238. Resilient rings, e.g., 22, 50 and 150 also facilitate axialmovement of teeth from ring 30, 130, 230 to ensure full engagement ofteeth 38, 138 or 238 and teeth 350 of teeth from split gripper assembly340. In one embodiment, bolt 215 is threadably received in a threadedhole on shaft 214.

Referring now to FIGS. 9 and 10, mechanical lock unit 10 may includerear lid 300. Rear lid 300 defines inner portion 302 and outer portion304. Inner portion 302 defines inside surface 306 and outer surface 308.Inside surface 306 surrounds first diameter portion 116 of shaft 114that is adjacent to first annular surface 120 of shaft 114. Outerportion 304 of rear lid 300 defines an inner surface 310 and a firstsurface 312. Although mechanical lock unit 10 is shown with secondembodiment components, e.g., shaft 114 and shaft lock assembly 112, itshould be understood that similar construction may be obtained by usingfirst embodiment components or third embodiment components that functionin a similar way.

Front lid 320 at least partially surrounds third diameter portion 119 ofshaft 114 and is adjacent to teeth form split gripper assembly 340.

Teeth form split gripper assembly 340 is retained between rear lid 300and front lid 320. Teeth form split gripper assembly 340 is located tosurround teeth form ring 130. Teeth form split gripper assembly 340 hasat least a first teeth form split gripper 342 (FIGS. 1A, 1B, 9, and 10)and a second teeth form split gripper 344 (FIGS. 1A, 1B). Spring 346(FIGS. 1A, 1B) is located between at least first teeth form splitgripper 342 and second teeth form split gripper 344 for biasing firstteeth form split gripper 342 away from second teeth form split gripper344. Springs 346 may be located between all teeth from split grippers inteeth from split gripper assembly 340.

First teeth form split gripper 342 and second teeth form split gripper344 define inner surface 348. Inner surface 348 defines a plurality ofteeth 350. Teeth 350 are provided for cooperative engagement withplurality of teeth 38, 138, and 238 of teeth form ring 30, 130, or 230.Teeth form split gripper assembly 340 additionally defines an outersurface 352 that defines at least one ramp 354. A flat run 355 may beadjacent to the ramp 354.

A spring loaded lock piston 360 includes a first sliding portion 362that defines a first end 364 and second ramp portion 366. Second rampportion 366 defines second end 368. The second end may include a secondflat run 367 adjacent to the second ramp portion 366. Flange portion 370extends outwardly. Flange portion 370 defines a first surface 372 and asecond surface 374. First sliding portion 362 surrounds and is insliding engagement with outer surface 308 of inner portion 302 of rearlid 300 and is also for sliding engagement with inner surface 310 ofouter portion 304 of rear lid 300. Second ramped portion 366 defines aninside surface for selective engagement with the at least one ramp 354on outer surface 352 of teeth form split gripper assembly 340. Secondflat run 367 and flat run 355 define another portion of the inside andouter surfaces respectively.

Biasing member 380 is provided adjacent to first end 364 of lock piston360 for biasing lock piston 360 towards engagement with teeth form splitgripper assembly 340.

Housing 390 defines a first portion that defines flange engaging surface396. Housing 390 defines a second portion that defines inside surface398 for engaging outside surface 376 of second ramped portion 366 ofspring loaded lock piston 360. Housing 390 defines a second surface 399.

Wherein first surface 372 of flange portion 370 of lock piston 360,flange engaging surface 396, and second surface 399 of housing 390define flange receiving area 397 for receiving flange portion 370 oflock piston 360.

A hydraulic force may be applied to the volume between second surface374 of flange portion 370 and second surface 399 at housing 390 forforcing lock piston 360 away from engagement with teeth form splitgripper assembly 340 thereby disengaging teeth form split gripper 342from contact with teeth form ring 38, 138, or 238 and establishing anunlocked configuration for mechanical lock unit 10.

A hydraulic force may be applied to the volume between first surface 372of flange portion 370 and first surface 312 of rear lid 300 as asafeguard for forcing lock piston 360 into engagement with teeth formsplit gripper assembly 340, thereby engaging teeth form split gripper342 into contact with teeth form ring 38, 138, or 238 and establishing alocked configuration for mechanical lock unit 10, 110 or 210.

In use, isolation plug 400 (FIGS. 6-8) is pigged through a pipeline toan isolation set location. Mechanical lock unit 10, 100, 210 or 410 isput into an unlocked state. Hydraulic pressure is applied to move plugcylinder 402 (FIG. 8) and attached shaft 14, 114, 414 for setting rubberpacker 404 (FIGS. 6-8). After packer 404 is fully set, the hydraulicforce inside mechanical lock unit 10, 100, 210, 410 is released so thata spring force of biasing member 380 pushes lock piston 360 ofmechanical lock unit 410 into a locked state. The engagement of teeth 38of teeth form ring 30, 130, or 230 and teeth 350 of teeth form splitgripper assembly 340, 440 holds the plug piston in place together withthe hydraulic force inside isolation plug 400.

In the normal locked state, the spring-loaded lock piston 360 inmechanical lock unit 10, 110, 210, 410 compresses springs 346 betweenteeth-form split grippers, e.g., between 342 and 344. Compression of theteeth-form split grippers causes teeth-form split grippers, e.g.,between 342 and 344, to engage with teeth-form ring 30, 130, or 230 thatholds and locks axial movement of shaft 14, 114, 414. In one embodiment,parallel, circumferential orientation of teeth 38, 138, or 238 and 350,rather than a threaded orientation, allows shaft 14 to rotate withoutlosing engagement. Horizontal contact at outer surface 352 between lockpiston 360 and teeth form split grippers, e.g., 342 and 344, as well asteeth engagement between teeth 38, 138, or 238 and 350, result intransferring all of the load of plug piston 402 held by rear lid 300 andfront lid 320 of mechanical lock unit 10, 100, 210, 410, which are verystrong.

To unlock mechanical lock unit 10, 100, 210, 410, a hydraulic force isapplied to spring-loaded lock piston 360 to overcome the force ofbiasing member 380 for pushing lock piston 360 into an unlockedposition. When there is no applied force from lock piston 360,teeth-form split grippers, e.g., 342 and 344, of teeth form splitgripper assembly 340 are lifted up by springs 346 between teeth formsplit grippers, e.g., 342 and 344. Teeth engagement between splitgrippers 342, 344 of teeth form split gripper assembly 340 and teethform ring 30, 130, or 230 on shaft 14 is, therefore, removed and shaft14 is unlocked and is free to move.

When mechanical lock 10, 100, 210, 410 is used in pipeline isolationtools, packers 404 form a seal with a pipeline wall 415 (FIGS. 7, 8),which results in a pressure disparity across the seal, i.e., the seal ofpackers 404 creates a high pressure side H and a low pressure side L(FIG. 8). The higher pressure on high pressure side H results in forcesthat act on the isolation tool that push on the isolation tool from highpressure side H towards low pressure side L. Mechanical lock 10, 100,210, 410 locks only in one direction, i.e., mechanical lock 10, 100,210, 410 locks the unset direction where the piston, comprised of shaft14 and piston head 402 moves toward the low pressure side L and the plugcylinder 403 moves toward the high pressure side H, which prevents unsetof packer 404. A compression spring, e.g., resilient ring 50 (FIG. 2) oranother spring member, is located adjacent to second end 34, 134 ofteeth-form ring 30, 130, 230. When mechanical lock 10, 100, 210, 410 isin a locked position (shown in FIG. 8) and there is high isolationpressure in the pipeline on the high pressure side H that creates alarge pressure differential across packers 404, Compression spring 50will be compressed to allow packers 404 to squeeze more (this isself-lock mode of the isolation tool). The self-lock mode increases thesealing capacity of the isolation tool under high isolation pressure.Thus, mechanical lock 10, 100, 210, 410 in pipeline isolation locksshaft 14 in one direction, and does not lock shaft 14 in the otherdirection to let packers 404 squeeze more in self-lock mode when thereis an isolation pressure in the pipeline.

In greater detail, when isolation plug 400 is set, shaft lock assembly112, 212 is locked, i.e., slips system 480 (FIG. 7) will grip the pipeand hold isolation plug 400 in place. Therefore, when set, structureconnected to slip system 480, e.g., shaft 14, 114, 214, and plug piston,comprised of shaft 14 and piston head 402, is held in place. Pressurefrom high pressure side H will push remaining components, includingteeth form ring 30, 130, 230 and teeth form split gripper assembly 340,towards low pressure side L, which forces packers 404 outwardly, i.e.,increases the squeeze packers 404. Mechanical lock is achieved bymechanical lock unit 10, 100, 210, 410, which holds teeth form ring 30,130, 230, when compression spring 50 is compressed. Compression ofcompression spring 50 results in an increase in the volume acting on thepiston cylinder 403, i.e., (V_(set)), which lowers the set pressure.This is referred to as self-lock mode.

The amount of movement, i.e., the increase in squeeze of packer 404, inself-lock mode depends on a difference between the force from isolationpressure and the original hydraulic set force, i.e., the pre-squeeze ofthe packer. Self-lock mode may be observed by a drop in the setpressure. At self-lock mode there will be a gap between first end 32,132 of teeth form ring 30, 130, 230, 430 and first annular surface 20,120, 220 of shaft 14, 114, 214 while second end 34, 134 of teeth formring 30, 130, 230 compresses compression spring 50. In the embodimentshown in FIGS. 8 and 9, movement of the teeth form ring 30, 130, 230leads to a drop of set pressure in self-lock mode. When the isolationpressure is removed, e.g., after an operation is complete, the setvolume, V_(set), will be restored to normal, which leads to restorationor increase in the set pressure. In self-lock mode, if set pressure islost, e.g., due to a leak inside the hydraulic system or due to losingoil inside the set volume, V_(set), the hydraulic lock will be lost.However, the isolation plug 400 will continue to seal since packer 404will continue to be squeezed by isolation pressure. Therefore, self-lockmode increases the safety level of isolation plug 400 in operation.Additionally mechanical lock will remain as a safe guard to self-lockmode since mechanical lock is achieved by teeth engagement.

Thus, the present invention is well adapted to carry out the objectivesand attain the ends and advantages mentioned above as well as thoseinherent therein. While presently preferred embodiments have beendescribed for purposes of this disclosure, numerous changes andmodifications will be apparent to those of ordinary skill in the art.Such changes and modifications are encompassed within the spirit of thisinvention as defined by the claims.

what is claimed is:
 1. A mechanical lock unit of a pipeline isolationtool comprising: a teeth-form ring for surrounding a shaft, saidteeth-form ring having a first end, a second end, a longitudinal axis,and an outer surface, said outer surface defining a plurality of teeththereon; a teeth-form split gripper assembly surrounding said teeth-formring, said teeth-form split gripper assembly having at least a firstteeth-form split gripper and a second teeth-form split gripper, saidfirst teeth-form split gripper and said second teeth form split gripperdefining an inner surface, said inner surface defining a plurality ofteeth for cooperative engagement with said plurality of teeth of saidteeth-form ring.
 2. The mechanical lock unit according to claim 1wherein: said teeth-form ring has a first part and a second part forfacilitating installation on a shaft.
 3. The mechanical lock unitaccording to claim 1 further comprising: a connector for joining saidfirst part and said second part of said teeth-form ring.
 4. Themechanical lock unit according to claim 1 wherein: said teeth-form ringdefines a slot for receiving a bolt for slidably retaining saidteeth-form ring on a shaft.
 5. The mechanical lock unit according toclaim 4 wherein said bolt is threadably received in a threaded hole insaid shaft.
 6. The mechanical lock unit according to claim 1 furthercomprising: a spring between said first teeth-form split gripper andsaid second teeth-form split gripper for biasing said first teeth-formsplit gripper away from said second teeth-form split gripper.
 7. Themechanical lock unit according to claim 1 wherein said plurality ofteeth on said teeth form ring and said plurality of teeth on said teethform split gripper assembly are parallel for allowing full rotation ofsaid teeth-form split gripper assembly with respect to said teeth-formring without losing engagement.
 8. The mechanical lock unit according toclaim 1 wherein: said teeth-form split gripper assembly has an outersurface that defines at least one ramp; and further comprising a lockpiston located for sliding parallel to said longitudinal axis, said lockpiston having a ramped portion defining an inside surface for selectiveengagement with said at least one ramp on said outer surface of saidteeth-form split gripper assembly for selectively pressing saidteeth-form split gripper assembly into contact with said a teeth-formring.
 9. A pipeline isolation tool comprising: a shaft having a plugcylinder affixed thereto; a packer activated by hydraulic pressure usedto move said plug cylinder and said shaft; a mechanical lock unit forsecuring a position of said shaft, said mechanical lock unit comprisinga teeth-form ring for surrounding said shaft, said teeth-form ringhaving a first end, a second end, a longitudinal axis, and an outersurface, said outer surface defining a plurality of teeth thereon; ateeth-form split gripper assembly surrounding said teeth-form ring, saidteeth-form split gripper assembly having at least a first teeth-formsplit gripper and a second teeth-form split gripper, said firstteeth-form split gripper and said second teeth form split gripperdefining an inner surface, said inner surface defining a plurality ofteeth for cooperative engagement with said plurality of teeth of saidteeth-form ring.
 10. The mechanical lock unit according to claim 9wherein: said teeth-form ring has a first part and a second part forfacilitating installation on a shaft.
 11. The mechanical lock unitaccording to claim 9 further comprising: a connector for joining saidfirst part and said second part of said teeth-form ring.
 12. Themechanical lock unit according to claim 9 wherein: said teeth-form ringdefines a slot for receiving a guide pin for slidably retaining saidteeth-form ring on a shaft for limiting axial travel of said teeth-formring on the shaft.
 13. The mechanical lock unit according to claim 9further comprising: a spring between said first teeth-form split gripperand said second teeth-form split gripper for biasing said firstteeth-form split gripper away from said second teeth-form split gripper.14. The mechanical lock unit according to claim 9 wherein said pluralityof teeth on said teeth form ring and said plurality of teeth on saidteeth form split gripper assembly are parallel for allowing fullrotation of said teeth-form split gripper assembly with respect to saidteeth-form ring without losing engagement.
 15. The mechanical lock unitaccording to claim 9 wherein: said teeth-form split gripper assembly hasan outer surface that defines at least one ramp; and further comprisinga lock piston located for sliding parallel to said longitudinal axis,said lock piston having a ramped portion defining an inside surface forselective engagement with said at least one ramp on said outer surfaceof said teeth-form split gripper assembly for selectively pressing saidteeth-form split gripper assembly into contact with said a teeth-formring.
 16. A method of securing a pipeline isolation tool in a pipelinecomprising: moving a piston for actuating the isolation tool, saidpiston affixed to a shaft; extending a slip assembly to engage a wall ofthe pipeline; extending a packer to engage the wall of the pipeline forcreating a high pressure on a high pressure side of the isolation tooland a low pressure on a low pressure side of the isolation tool;engaging said shaft with a mechanical lock; compressing a compressionspring with said high pressure by moving said cylinder towards said lowpressure side; wherein said moving of said cylinder increases a setvolume, which lowers a set pressure for effecting a self-lock mode. 17.The method according to claim 16 wherein: said mechanical lock comprisesa teeth-form ring for surrounding said shaft, said teeth-form ringhaving a first end, a second end, a longitudinal axis, and an outersurface, said outer surface defining a plurality of teeth thereon; ateeth-form split gripper assembly surrounding said teeth-form ring, saidteeth-form split gripper assembly having at least a first teeth-formsplit gripper and a second teeth-form split gripper, said firstteeth-form split gripper and said second teeth form split gripperdefining an inner surface, said inner surface defining a plurality ofteeth for cooperative engagement with said plurality of teeth of saidteeth-form ring.